1. Field of the Invention
This invention relates to wireless communication systems, and more particularly to a method and apparatus for efficiently allocating bandwidth between base stations and users in a wireless communication system.
2. Description of Related Art
Recently, wideband or “broadband” wireless communications networks have been proposed for providing delivery of enhanced services such as voice, data and video services. The broadband wireless communication system facilitates two-way communication between a base station and a plurality of fixed subscriber stations or Customer Premises Equipment (CPE) stations. One exemplary broadband wireless communication system is described in related U.S. Pat. No. 6,016,311, and shown in block diagram of FIG. 1.
As described in related U.S. Pat. No. 6,016,311, a wireless communication system facilitates two-way communication between plurality of subscriber radio stations or subscriber units (fixed or portable) and a fixed network infrastructure. Exemplary communication systems include mobile cellular telephone systems, personal communication systems (PCS), and cordless telephones. A key objective of these wireless communication systems is to provide communication channels on demand between a plurality of user units and one or more associated base stations in order to connect a subscriber or user with a network infrastructure (such as the Internet). Both wired and wireless systems, however, may have multiple access schemes which permit a particular user to obtain access to a shared communication media, such as a particular physical radio channel. Many of such shared media systems divide access between various users by allocating timeslots within a time “frame,” which is used as a basic information transmission unit. Each frame is typically sub-divided into a plurality of time slots, which may be synchronous or asynchronous within the frame, some of which are used for control purposes and some for information transfer.
Bidirectional communication units typically use a “duplexing” scheme to allow information flow in both directions. Transmissions from the base station to users are commonly referred to as “downlink” transmissions. Transmissions from a user to the base station are commonly referred to as “uplink” transmissions. Time division duplexing (TDD) and frequency division duplexing (FDD) methods are examples of duplexing schemes to facilitate the exchange of information both directions between base stations and users.
As shown in FIG. 1, the exemplary broadband wireless communication system 100 includes a plurality of cells 102. Each cell 102 contains an associated cell site 104 that primarily includes a base station 106 and an active antenna array 108. Each cell 102 provides wireless connectivity between the cell's base station 106 and a plurality of customer premises equipment (CPE) 110 positioned at fixed customer sites 112 throughout the coverage area of the cell 102. The users of the system 100 may include both residential and business customers. Each cell may service several hundred or more residential and business users.
The type and quality of services available to the customers are variable and selectable. Different broadband services have different bandwidth and latency requirements, depending on the information rate and the quality of service they provide. For example, T1-type continuous bit rate (CBR) services typically require bandwidth sufficient to communicate at a well-defined data rate which has well-controlled delivery latency. Until terminated, these services generally require bandwidth allocation at a constant rate. In contrast, certain other types of data services, such as Internet protocol data services, are bursty, frequently idle (momentarily requiring zero bandwidth), and are relatively insensitive to delay variations when active.
Due to the wide variety of user service requirements, and due to the large number of users serviced by any one base station, the bandwidth allocation process in a broadband wireless communication system such as that shown in FIG. 1 can become burdensome and complex. This is especially true with regard to the allocation of uplink bandwidth. Base stations do not have a priori information regarding the bandwidth or quality of services that a selected user will require at any given time. Consequently, requests for changes to the uplink bandwidth allocation are necessarily frequent and varying. Due to this volatility in the uplink bandwidth requirements, the many CPEs serviced by a selected base station will frequently need to request bandwidth allocation. If uncontrolled, the bandwidth allocation requests will detrimentally affect system performance. The bandwidth required to accommodate user bandwidth allocation requests can become disproportionately high in comparison with the bandwidth allocated for the transmission of substantive data traffic, reducing the communication system bandwidth available to provide broadband services. This principle applies to most communications systems which share a limited communication medium among varying user connections.
Therefore, a need exists for a method and apparatus that can dynamically and efficiently allocate bandwidth in response to varying bandwidth needs in a shared media communication system. The method and apparatus should be responsive to the needs of a particular communication link. The bandwidth allocation method and apparatus should be efficient in terms of the amount of system bandwidth consumed by the actual bandwidth request and allocation process. That is, the bandwidth requests generated by the user should consume a minimum percentage of available uplink bandwidth. In addition, the bandwidth allocation method and apparatus should respond to bandwidth requests in a timely manner. Bandwidth should be allocated to high priority services in a sufficiently short time frame to maintain the quality of service specified by the user. Further, the bandwidth allocation method and apparatus should be capable of processing an arbitrarily large number of bandwidth allocation requests from a relatively large number of users. For example, in the system shown in FIG. 1, over one hundred users may be allowed to be simultaneously active, coordinating their transmissions on the uplink. The exemplary system can accommodate approximately one thousand CPEs on the physical channel.
Some prior art systems have attempted to solve bandwidth allocation requirements in a system having a shared system resource by maintaining logical queues associated with the various data sources requiring access to the shared system resource. Such a prior art system is taught by Karol et al., in U.S. Pat. No. 5,675,573, that issued on Oct. 7, 1997. More specifically, Karol et al. teach a bandwidth allocation system that allows packets or cells within traffic flows from different sources that are contending for access to a shared processing fabric to get access to that fabric in an order that is determined primarily on individual guaranteed bandwidth requirements associated with each traffic flow. In addition, the system taught by Karol et al. allow the different sources to gain access to the shared processing fabric in an order determined secondarily on overall system criteria, such as a time of arrival, or due date of packets or cells within the traffic flows. Packets or cells of data from each data source (such as a bandwidth requesting device) are queued in separate logical buffers while they await access to the processing fabric.
A need exists for efficient bandwidth allocation methods which accommodate an arbitrarily large number of users having uplink bandwidth needs which vary frequently. The inventors have recognized that in order to efficiently allocate bandwidth, it is important to determine the bandwidth needs of users in a timely, accurate and efficient manner.